Wellbore plug structure and method for pressure testing a wellbore

ABSTRACT

A wellbore plug structure and a method for pressure testing a wellbore using the plug structure. The plug structure advantageously allows pressure testing of the wellbore casing without the use of a toe sleeve and without requiring the application of a pressure in excess of the wellbore pressure test after testing is completed. The wellbore plug structure includes a piston member that can be released at any time after placement of the structure in the wellbore casing to expose a dissolvable element to a pressurizing fluid. A pressure test may then be conducted before the fluid completely dissolves the dissolvable element. Once the dissolvable element is dissolved, a fluid pathway through the wellbore plug structure is created that many enable the placement of tooling through the plug structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of U.S. Provisional Patent Application No. 62/375,203, filed on Aug. 15, 2016, the disclosure of which is incorporated herein by reference in its entirety.

FIELD

This disclosure relates to the field of wellbore plugs, such as wellbore plugs that are used for the construction and/or use of a wellbore for the extraction of natural resources from the earth, such as oil, gas, water and the like.

BACKGROUND

In the downhole drilling industry, e.g., for oil and gas extraction, it is common practice to drill a borehole and install a casing in the borehole to form a well. The casing is commonly cemented into the borehole, which may include pumping a wiper plug down the casing to force the cement through a port located at a distal end of a casing string. After completion of the cementing operation, it is often necessary to conduct an integrity test on the casing before fracturing operations to ensure that the casing can safely withstand operating pressures without failure. Commonly, such pressure tests are performed against a pressure-activated toe sleeve disposed at the bottom (e.g., the toe) of the casing. However, after the pressure test, a flow path must be formed through the toe sleeve by using a pressure in excess of the test pressure, thereby invalidating the initial pressure test. Also, the toe sleeve against which a pressurization test is conducted often has an atmospheric chamber. The applied pressure may allow fluid to move past the O-ring and into the atmospheric chamber, which would either prematurely open the sleeve or prevent the sleeve from opening after the pressure test.

SUMMARY OF THE INVENTION

There is a need for a wellbore plug structure that enables a full pressure test of the wellbore casing to be performed without the use of a pressure activated toe sleeve, and/or without requiring the application of a pressure in excess of the pressure test pressure to begin the fracturing process.

The present disclosure relates to a wellbore plug structure, such as a wiper plug, that advantageously allows a full pressure test of the casing to be performed against the plug structure, without the need for a toe sleeve. With the disclosed wellbore plug structure, the pressure test does not have to occur against an atmospheric chamber.

In one embodiment, a wellbore plug structure is disclosed. The wellbore plug structure includes a tubular member defining a longitudinally-extending fluid conduit having a proximal fluid inlet and a distal fluid outlet, a wiping member disposed around the tubular member, a piston member comprising a piston body that is at least partially disposed in the fluid conduit, and a temporary fluid stopper comprising a dissolvable fluid obstructing portion, where the dissolvable fluid obstructing portion is disposed in spaced-apart relation from the piston member toward the distal fluid outlet. The piston member and the dissolvable fluid obstructing portion define an interior chamber within the fluid conduit, the interior chamber being fluidly sealed from the proximal fluid inlet by the piston member and being fluidly sealed from the distal fluid outlet by the dissolvable fluid obstructing portion.

In one characterization, the piston member is configured to release and move toward the distal fluid outlet when the piston member is exposed to a pressure difference across the piston member that is equal to or greater than a piston release pressure. The release and movement of the piston member creates a fluid pathway from the proximal fluid inlet to the interior chamber of the fluid conduit. The piston member may include at least one shear element, wherein the at least one shear element operatively secures the piston member within the fluid conduit and is configured to shear when the piston member is exposed to the pressure difference across the piston member that is equal to or greater than the piston release pressure to release the piston body. At least a second shear element may be provided in the piston member. The shear element(s) may be a shear screw.

In certain characterizations, the piston member is fully disposed within the fluid conduit. The piston body may be fabricated from a metallic material, such as aluminum. The piston body may be substantially cylindrical, such as to operatively fit within a cylindrical fluid conduit. The piston member may include a sealing component disposed around an outer circumference of the piston body, such as one or more elastomeric O-rings.

In another characterization, the wiping member includes at least a first wiper blade extending radially from the tubular member, and the at least the first wiper blade may be fabricated from a flexible elastomeric material.

In another characterization, wherein the tubular member is fabricated from a metal, such as from aluminum, e.g., an aluminum alloy.

In yet another characterization, the dissolvable fluid obstructing portion is disposed across the fluid conduit. In another characterization, the dissolvable fluid obstructing portion is fabricated from a material that is dissolvable in an aqueous medium, e.g., in an aqueous chloride solution or in fresh water. The dissolvable fluid obstructing portion is fabricated from a metallic material, such as from a magnesium alloy. In another characterization, the dissolvable fluid obstructing portion is fabricated from a polymeric material. The dissolvable fluid obstructing portion may have a thickness measured along a central longitudinal axis of the fluid conduit that is at least about 0.5 mm, and that is not greater than about 300 mm, such as not greater than about 100 mm.

In another characterization, the dissolvable fluid obstructing portion abuts a distal material chamber on a side opposite the interior chamber. A cap member may abut the distal material chamber on a side opposite the dissolvable fluid obstructing portion, and the distal material chamber may be substantially filled with a hydrophobic material, such as with grease.

The wellbore plug structure may further include a landing arrangement disposed at a distal end of the wellbore plug structure that is configured to operatively engage a latch collar that is disposed in a wellbore, i.e., is disposed in the casing.

In one characterization of the temporary fluid stopper, the stopper includes a cup-like temporary fluid stopper body having a dissolvable fluid obstructing portion and a wall portion extending from a circumferential edge of the dissolvable fluid obstructing portion along an interior wall of the fluid conduit. A sealing component, such as an elastomeric O-ring, may be disposed around the temporary fluid stopper body, e.g., where the sealing component abuts against an interior wall of the fluid conduit. In this characterization, the temporary fluid stopper body and the dissolvable fluid obstructing portion comprise the dissolvable material, e.g., are fabricated from the dissolvable material.

In another characterization, the dissolvable fluid obstructing portion comprises a dissolvable disk body, e.g., a dissolvable disk body that is disposed across the longitudinally-extending fluid conduit. The dissolvable disk body may also be disposed across the distal fluid outlet, such as where the dissolvable disk body is secured to a landing arrangement disposed at a distal end of the wellbore plug structure, the landing arrangement being configured to operatively engage a latch collar disposed in a wellbore. The temporary fluid stopper may include a sealing component disposed around an outer edge of the dissolvable disk body, such as an elastomeric O-ring.

In one characterization of the fluid conduit, the conduit includes at least a first conduit portion and a second conduit portion, the second conduit portion having a larger diameter than the first conduit portion, wherein the first conduit portion is disposed near the proximal end of the fluid conduit and wherein the piston member is at least partially disposed within the first conduit portion.

The foregoing embodiments relate to a structure wherein the dissolvable material serves as the physical barrier to fluid flow through the wellbore plug structure. In another embodiment, a wellbore plug structure is disclosed that includes a tubular member defining a longitudinally-extending fluid conduit having a proximal fluid inlet and a distal fluid outlet, a wiping member disposed around the tubular member, a piston member comprising a piston body that is at least partially disposed in the fluid conduit, and a collet member at least partially disposed within the fluid conduit, the collet member comprising a collet member body, the collet member body comprising a plurality of collet fingers, and a dissolvable ring component disposed within the collet body to resist inward collapse of the collet fingers. The collet member and the piston member define an interior chamber within the fluid conduit, the interior chamber being fluidly sealed from the proximal fluid inlet by the piston member and being fluidly sealed from the distal fluid outlet by the collet member.

In one characterization of the piston member, the piston member is configured to release and move toward the distal fluid outlet when the piston member is exposed to a pressure difference across the piston member that is equal to or greater than a piston release pressure. The release and movement of the piston member may create a fluid pathway from the proximal fluid inlet to the interior chamber of the fluid conduit. In certain characterizations, the piston member includes at least one shear element (e.g., two or more shear elements), where the shear element(s) operatively secure the piston member within the fluid conduit and are configured to shear when the piston member is exposed to the pressure difference across the piston member that is equal to or greater than the piston release pressure to release the piston body. The shear elements may include, e.g., a shear screw. The piston member may be fully disposed within the fluid conduit, and the piston body may be fabricated from a metallic material such as aluminum. The piston body may be substantially cylindrical, and the piston member may include a sealing component disposed around an outer circumference of the piston body, such as an elastomeric O-ring.

In one characterization of the wiping member, the wiping member includes at least a first wiper blade extending radially from the tubular member. The first wiper blade may be fabricated from a flexible elastomeric material.

In one characterization of the tubular member, the tubular member is fabricated from a metallic material, such as from aluminum.

In one characterization of the collet member body, the collet member body is fabricated from a metallic material, such as from aluminum. The collet member may include a sealing component disposed around an outer circumference of the collet member body, such as one or more elastomeric O-rings.

In another embodiment of the present disclosure, a method of pressure testing a wellbore is disclosed. The method may include the use of any of the wellbore plug structures described herein. In one characterization, the method includes the steps of inserting a wellbore plug structure into a wellbore casing, the wellbore plug structure comprising a tubular member defining a longitudinally-extending fluid conduit having a proximal fluid inlet and a distal fluid outlet. The wellbore plug structure also includes a wiping member disposed around the tubular member, such as for wiping the casing during insertion of the wellbore plug structure into the wellbore. A piston member comprising a piston body is at least partially disposed in the fluid conduit, and a temporary fluid stopper comprising a dissolvable element is disposed in the fluid conduit, where the dissolvable element is configured to directly or indirectly form a seal with the fluid conduit. The wellbore casing is pressurized to a first wellbore pressure to advance the wellbore plug structure down the well bore, and is pressurized to a second wellbore pressure that is greater than the first wellbore pressure, such as by using a pressurization fluid, wherein the second wellbore pressure displaces the piston member into the fluid conduit and exposes the dissolvable element to the pressurizing fluid. A pressurization test (e.g., a casing integrity test) may then be performed at a third wellbore pressure before the pressurizing fluid completely dissolves the dissolvable element, thereby creating a fluid pathway through the wellbore pressure.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a wellbore plug structure according to an embodiment of this disclosure.

FIG. 2 illustrates a cross-sectional view of a wellbore plug structure according to another embodiment of this disclosure.

FIG. 3 illustrates a cross-sectional view of a wellbore plug structure according to another embodiment of this disclosure.

FIG. 4 illustrates a cross-sectional view of a wellbore plug structure according to another embodiment of this disclosure.

FIG. 5 illustrates a cross-sectional view of a wellbore plug structure according to another embodiment of this disclosure.

DESCRIPTION OF THE EMBODIMENTS

The present disclosure is directed to wellbore plug structures and methods of pressure testing a wellbore, e.g., methods utilizing wellbore plug structures having the relevant operational characteristics of the wellbore plug structures disclosed herein.

Generally, a wellbore plug structure according to certain embodiments of the present disclosure includes a tubular member, a wiping member disposed around the tubular member, and a piston member that is at least partially disposed in the tubular member. The piston member is configured to prevent a fluid from contacting a dissolvable component of the wellbore plug structure until the piston member is moved under the force of pressure to create a fluid pathway to the dissolvable component. In one embodiment, a temporary fluid stopper includes a dissolvable fluid obstructing portion, and the piston member releases (e.g., moves downward) to expose the dissolvable fluid obstructing portion to a fluid. In this regard, the tubular member defines a longitudinally-extending fluid conduit having a proximal fluid inlet and a distal fluid outlet. The piston member includes a piston body that is at least partially disposed in the fluid conduit. The dissolvable fluid obstructing portion is disposed in spaced-apart relation from the piston member and toward the distal fluid outlet. The piston member and the dissolvable fluid obstructing portion define an interior chamber within the fluid conduit, the interior chamber being fluidly sealed from the proximal fluid inlet by the piston member and being fluidly sealed from the distal fluid outlet by the dissolvable fluid obstructing portion.

In other embodiments, the wellbore plug structure includes a tubular member defining a longitudinally-extending fluid conduit having a proximal fluid inlet and a distal fluid outlet. The piston member including a piston body is at least partially disposed in the fluid conduit, and a collet member is at least partially disposed within the fluid conduit and includes a collet member body and a dissolvable ring component disposed around an interior surface of the collet body. When the piston moves it exposes the dissolvable ring component to the fluid, thereby dissolving the ring and enabling collet member fingers to move inwardly such that the collet body can be moved down the fluid conduit to create a fluid pathway through the wellbore plug structure.

As is noted above, one of the aspects of the wellbore plug structure is the presence of one or more components (e.g., the dissolvable fluid obstructing portion) that is fabricated from a dissolvable material. As used herein, the term dissolvable and its conjugates (e.g., dissolve, dissolved, etc.) refer broadly to any mechanism by which a unitary (e.g., intact) body or component will break down, rapidly corrode, disintegrate, etc., irrespective of the actual mechanism, e.g., irrespective of whether or not the material wholly or partially solubilizes in the fluid. Examples of dissolvable materials include, but are not limited to, magnesium alloys such as those that are sold under the tradename TervAlloy (Terves, Inc., Euclid, Ohio), and magnesium alloys sold under the tradename SoluMag (Magnesium Elektron North America, Madison, Ill.). Other useful dissolvable materials, including aluminum alloys, are disclosed in U.S. Pat. No. 8,770,261 by Marya and U.S. Pat. No. 8,211,247 by Marya et al., each of which is incorporated herein by reference in its entirety. Other useful dissolvable materials may include certain polymers, such as biodegradable thermoplastics, an example of which is polyglycolic acid (PGA). As is known to those skilled in the art, the dissolvable material may be selected for its rate of dissolution, e.g., a “slow” dissolution rate vs. a “fast” dissolution rate. The dissolvable material may comprise a composite of two or more materials, e.g., where one material phase is dispersed throughout another material phase or where the material is in the form of a multi-layer structure of different materials. Without limiting the present disclosure, such dissolvable materials are dissolvable in an aqueous medium, such as in freshwater and/or in a weak chloride solution (e.g., KCl, HCl, etc.). The dissolvable material may have a dissolution rate in the range of from about 30 mg/cm²·hr to about 1000 mg/cm²·hr in such aqueous mediums at about 200° F.

Referring now to FIG. 1, a wellbore plug structure 100 according to one embodiment of the present disclosure is illustrated in cross-section. The wellbore plug structure 100 is generally configured to be operatively disposed down a wellbore, e.g., during the formation of a bore in the earth's surface for the extraction of oil, natural gas, or other natural resources. In this regard, the wellbore plug structure 100 includes a tubular member 102. The tubular member 102 comprises a substantially cylindrical shape and defines a longitudinally-extending fluid conduit 110 extending through a central portion of the tubular member 102. The fluid conduit 110 includes a proximal fluid inlet 112 at a proximal end of the fluid conduit 110 and a distal fluid outlet 114 disposed at a distal end of the fluid conduit 110. A wiping member 104 is disposed around the tubular member 102 and is configured to wipe the sidewall of the wellbore casing when the wellbore plug structure 100 is displaced (e.g., moved) down the wellbore casing.

A piston member 106 includes a piston body 116 that is disposed (e.g., at least partially disposed) in the longitudinally-extending fluid conduit 110. Also disposed within the fluid conduit 110 is a temporary fluid stopper 108 that includes a temporary fluid stopper body 140 having a dissolvable fluid obstructing portion 118, where the dissolvable fluid obstructing portion 118 is disposed in spaced-apart relation from the piston member 106 (e.g., in spaced-apart relation from the piston body 116) toward the distal fluid outlet 114. The piston member 106 and the dissolvable fluid obstructing portion 118 define an interior chamber 120 within the fluid conduit 110, e.g., that is bounded by the dissolvable fluid obstructing portion 118, a wall portion 142 of the temporary fluid stopper 108, and the piston member 106. Thus, the interior chamber 120 is fluidly sealed from the proximal fluid inlet 112 by the piston member 106 and is fluidly sealed from the distal fluid outlet 114 by the dissolvable fluid obstructing portion 118.

In this embodiment, the piston body 116 is configured to release and move toward the distal fluid outlet 114 when the piston member 106 is exposed to a pressure difference across the piston member 106 that is equal to or greater than a piston body release pressure, e.g., a predetermined piston body release pressure. The release and movement of the piston body 116 under this condition creates a fluid pathway from the proximal fluid inlet 112 to the interior chamber 120. Typically, the pressure difference across the piston member 106 is created by a pressurized fluid (e.g., a pressurized liquid) that is applied to the proximal end of the wellbore plug structure 100 when the wellbore plug structure 100 is disposed in a wellbore casing and is sealed against the sidewall of the wellbore casing by the wiping member 104. Thus, when the piston body 116 releases, the pressurized fluid will enter the longitudinally-extending fluid conduit 110 through the proximal fluid inlet 112 and come into contact with the temporary fluid stopper 108. Typically, the interior chamber 120 will be at or very near ambient pressure, although the interior chamber 120 could be at a pressure less than ambient or more than ambient as may be desired, e.g., to facilitate movement of the piston member by the pressurized fluid.

In this regard, the piston body release pressure will typically be greater than ambient pressure. It will be appreciated that the wellbore plug structure, particularly the structure of the piston member, may be configured such that the piston body release pressure is well-controlled and may vary over a wide range of pressures. In certain characterizations, the piston body release pressure will be at least about 250 psi (pounds per square inch), such as at least about 4000 psi.

Thus, the piston member 106 is configured and placed relative to the longitudinally-extending fluid conduit 110 such that the piston member 106 maintains a fluid seal until such time as a pressure, greater than or equal to the piston body release pressure, is applied to the piston member 106. In this regard, the piston body 116 may be precisely sized such that the outer circumference of the piston body 116 forms a fluid tight seal against the interior wall 126 of the fluid conduit 110, or against a sleeve member 162 that is disposed between the piston body 116 and the interior wall 126 of the fluid conduit 110, such that the piston body 116 frictionally resists movement until the piston body release pressure is reached. A portion of the piston body may also extend upwardly and over the upper circumference of the sleeve member (e.g., as a flange) to resist pressure until the flange collapses. In another characterization, and as is illustrated in FIG. 1, the piston member 106 may include at least one shear element 124 a, wherein the at least one shear element 124 a operatively secures the piston body 116 within the fluid conduit 110. The shear element 124 a may comprise a shear pin, shear ring, or shear wire. In one particular characterization, the shear element comprises a shear screw. Further, the piston member 106 may include more than one shear element, such as shear elements 124 a and 124 b. The shear element(s) 124 a/124 b are configured to shear when the piston member 106 is exposed to the pressure difference across the piston member 106 that is equal to or greater than the piston body release pressure, thereby releasing the piston body 116.

As is illustrated in the embodiment of FIG. 1, the piston member 106 is fully disposed within the fluid conduit 110. However, it is contemplated that the wellbore plug structure 100 may be configured such that the piston member 106 is only partially disposed within the fluid conduit 110, e.g., where a proximal portion of the piston member 106 extends upwardly beyond the proximal fluid inlet 112.

The piston body 116 may be fabricated from virtually any material. For example, it is contemplated that the entire piston body 116, or at least a portion of the piston body 116, may be fabricated from a dissolvable material, e.g., a material that is capable of dissolution in an aqueous and/or a saline aqueous solution as is discussed above. In certain characterizations, the piston body 116 is at least partially fabricated from a metallic material, particularly a millable metallic material such as aluminum or cast-iron. In this regard, for certain applications, it may be preferable to utilize a piston body that is at least partially fabricated from aluminum. As used herein, the term aluminum encompasses both pure aluminum and aluminum alloys, e.g., alloys that comprise at least about 50% aluminum. The piston body 116 may be substantially cylindrical, such as to operatively fit within a substantially cylindrical longitudinally-extending fluid conduit 110, or, as illustrated in FIG. 1, within a sleeve member 162 that itself is disposed within the fluid conduit 110. To ensure a substantially fluid tight seal between the piston body 116 the interior side wall 126 of the longitudinally-extending fluid conduit 110, the piston body 116 may include a sealing component 130, e.g., a sealing component that is disposed around an outer circumference of the piston body 116. The sealing component 130 may comprise configurations such as a Chevron-type seal. In certain characterizations, the sealing component 130 comprises an elastomeric O-ring. Further, the piston member 106 may include more than one sealing component 130, such as a plurality of elastomeric O-rings that are disposed around the piston body 116. Although the embodiment illustrated in FIG. 1 illustrates the use of an elastomeric O-ring as the sealing component 130, the piston body 116 may be configured, e.g., precision machined, to a tight tolerance such that a metal-to-metal seal may be formed between the piston body 116 and the interior surface of the longitudinally-extending fluid conduit 110. Further, although illustrated as comprising a sealing component that is operatively affixed to the piston body 116, a sealing component may also be fixed to an interior of the longitudinally-extending fluid conduit 110 to form a seal between the piston body 116 and the interior wall 126 of the fluid conduit, or to the sleeve member 162.

As can be seen from the wellbore plug structure 100 illustrated in FIG. 1, the piston member 106 fluidly seals the interior chamber 120 of the longitudinally-extending fluid conduit 110 from the proximal fluid inlet 112. Thus, when a fluid (e.g., a liquid or slurry) is pressurized against the piston member 106 at a pressure that is less than the piston body release pressure, the piston member 106 will prevent fluid from entering the interior chamber 120 and from contacting the temporary fluid stopper 108, particularly from contacting the dissolvable fluid obstructing portion 118 of the temporary fluid stopper 108.

To ensure that the fluid pressure applied above the wellbore plug structure 100 is applied upon the piston member 106, the wiping member 104 may include at least a first wiper blade 134 a that extends radially from the tubular member 102 to form a tight seal against the casing when the wellbore plug structure is placed down the casing. The wiping member 104 may include additional wiper blades, such as wiper blade 134 b. As is illustrated in FIG. 1, the wiping member 104 comprises four wiper blades that extend radially from the tubular member 102. The wiping member 104 may be integrally formed with the tubular member 102, or may be a separate component that is attached to the tubular member 102. The size of the wiper blades (e.g., outer diameter of the wiper blades) is configured to form a tight fluid seal when the wellbore plug structure 100 is placed down a wellbore casing. In this regard, the wiper blades may be fabricated from a flexible elastomeric material in order to form such a fluid-tight seal. During certain operations, the wiper blades may also force material that is loosely adhered to the interior wall of the wellbore casing down the wellbore casing, e.g., may force wet, flowable cement down the casing during a wellbore cementing operation.

The tubular member 120 may be fabricated from a variety of materials and in certain characterizations the tubular member is fabricated (e.g., machined) from a metallic material, such as aluminum. It will be appreciated that the fluid conduit 110 will have a diameter that is sufficiently large to accommodate tooling to be placed through the fluid conduit after removal of the piston member 108 and the fluid obstructing portion 118. The wellbore plug structure 100 may also include a landing arrangement 136 disposed at a distal end of the wellbore plug structure 100, e.g., at a distal end of the tubular member 102. The landing arrangement 136 is configured to operatively engage with a latch collar (e.g., a sealing latch collar) or similar structure that is disposed near the bottom of the wellbore. Such landing arrangements are known to those of ordinary skill in the art.

The temporary fluid stopper 108 includes a dissolvable fluid obstructing portion 118. The dissolvable fluid obstructing portion 118 is disposed in spaced-apart relation from the piston member 106 (e.g., from the piston body 116) toward the distal fluid outlet 114. As illustrated in FIG. 1, the dissolvable fluid obstructing portion 118 is disposed across the fluid conduit 110. The dissolvable fluid obstructing portion 118 is fabricated from a dissolvable material, e.g., that is dissolvable in the fluid that comes into contact with the dissolvable fluid obstructing portion 118 when the piston body 116 releases and creates a fluid pathway from the proximal fluid inlet 112 to the fluid obstructing portion 118.

As illustrated in FIG. 1, the temporary fluid stopper 108 is cup-like (e.g., cup-shaped) and includes a dissolvable fluid obstructing portion 118 and a wall portion 142 extending from a circumferential edge of the dissolvable fluid obstructing portion 118 toward the proximal inlet 112. Although illustrated in FIG. 1 as having a cup-like configuration, it will be appreciated that the temporary fluid stopper may have any configuration (e.g., shape) to fit within the fluid conduit 110 and to temporarily obstruct fluid flow upon release of the piston body 116.

In the embodiment of FIG. 1, substantially the entire temporary fluid stopper 108 (e.g., the wall portion 142 and the fluid obstructing portion 118) is fabricated from a dissolvable material. Thus, in this embodiment, when the piston body 116 is displaced toward the distal end of the fluid conduit 110, the wall portion 142 is exposed to the fluid and begins to dissolve. In addition, because the outer circumference of the piston body 116 is less than an inner diameter of the wall portion 142, a fluid pathway will also form around the piston body 116 such that the fluid obstructing portion 118 will also begin to dissolve. Over a period of time, the fluid will dissolve and “eat through” the wall portion 142 and the fluid obstructing portion 118. The thickness of the wall portion 142 and/or of the fluid obstructing portion 118 may be selected to maintain a degree of control over the time that is needed to dissolve through the fluid stopper body 140.

As is illustrated in the embodiment of FIG. 1, the temporary fluid stopper 108 also includes a sealing component 150 that is disposed around the wall portion 142 of the temporary fluid stopper body 140. In this regard, the sealing component 150 abuts and seals against an inner surface of the tubular member 102, i.e., against an inner surface of the longitudinally-extending fluid conduit 110. As with the sealing component 130, the sealing component 150 may be of any configuration, and in one characterization is an elastomeric O-ring. Further, a distal material chamber 154 is disposed between the fluid obstructing portion 118 and a distal fluid outlet 114, and includes a hydrophobic material 158 (e.g., grease) to prevent liquids from prematurely contacting the dissolvable material that constitutes the fluid obstructing portion 118.

Thus, when the piston body 116 releases it drops into the interior chamber 120 and exposes the dissolvable material (e.g., the temporary fluid stopper 108) to the fluid.

FIG. 2 illustrates a cross-sectional view of a further embodiment of a wellbore plug structure 200 according to the present disclosure. Those components of the wellbore plug structure 200 that are illustrated but not described in detail are similar to the components of the wellbore plug structure 100 described above with respect to FIG. 1, and the components may be constructed from similar materials and in similar fashion as those components described with respect to FIG. 1.

The wellbore plug structure 200 is also configured to be operatively disposed down a wellbore. The wellbore plug structure 200 includes a tubular member 202 having a substantially cylindrical shape and defining a longitudinally-extending fluid conduit 210 extending through a central portion of the tubular member 202. The fluid conduit 210 includes a proximal fluid inlet 212 at a proximal end of the fluid conduit 210 and a distal fluid outlet 214 disposed at a distal end of the fluid conduit 210. A wiping member 204 is disposed around the tubular member 202 and is configured to wipe the sidewall of the wellbore casing when the wellbore plug structure 200 is displaced down the wellbore casing.

A piston member 206 includes a piston body 216 that is disposed (e.g., at least partially disposed) in the longitudinally-extending fluid conduit 210. Also disposed within the fluid conduit 210 is a temporary fluid stopper 208 that comprises a dissolvable disk body 240, i.e., that is fabricated from a dissolvable material. The dissolvable disk body 240 is disposed in spaced-apart relation from the piston member 206 (e.g., in spaced-apart relation from the piston body 216) toward the distal fluid outlet 214. The piston member 206 and the dissolvable disk body 240 define an interior chamber 220 within the fluid conduit 210, e.g., that is bounded by the interior wall 226 of the fluid conduit 210, by the dissolvable disk body 240, and by the piston member 206. As a result, the interior chamber 220 is fluidly sealed from the proximal fluid inlet 212 by the piston member 206 and is fluidly sealed from the distal fluid outlet 214 by the dissolvable disk body 240. The dissolvable disk body 240 is protected from moisture by a hydrophobic material 258 that is retained by a disk 260 (e.g., a plastic disk) at a distal end of the landing arrangement 236.

As with the embodiment described above with respect to FIG. 1, the piston body 216 is configured to release and move toward the distal fluid outlet 214 when the piston member 206 is exposed to a pressure difference across the piston member 206 that is equal to or greater than the piston body release pressure. The release and movement of the piston body 216 creates a fluid pathway from the proximal fluid inlet 212 to the interior chamber 220. In this regard, the longitudinally-extending fluid conduit 210 includes a first conduit portion 210 a and a second conduit portion 210 b where the second portion 210 b has a diameter that is greater than the diameter of the piston body 216 and is greater than the diameter of the first portion 210 a. Thus, when the piston body 216 is released and drops into the second portion 210 b of the fluid conduit 210, a fluid pathway is created, e.g., around the piston body 216.

As illustrated in FIG. 2, the temporary fluid stopper 208 includes a dissolvable disk body 240 that extends across the fluid conduit 210. A sealing component 250 (e.g., an elastomeric O-ring) is provided to form a tight seal against an interior surface of the landing arrangement 236. The thickness of the dissolvable disk body 240 (e.g., along a longitudinal axis of the fluid conduit 210) may be selected to achieve a desired dissolution time. As illustrated in FIG. 2, an outer periphery of the disk body 240 has a greater thickness to reduce the possibility of the disk body 240 failing (e.g., fracturing) prematurely such as due to the impact of the piston body 216.

Compared to the embodiment illustrated in FIG. 1, the temporary fluid stopper 208 utilizes less dissolvable material than the temporary fluid stopper 108. Further, the inner diameter of the fluid conduit 210 may be larger than the fluid conduit 110, enabling better fluid flow.

FIG. 3 illustrates another embodiment of a wellbore plug structure according to the present disclosure. Those components of the wellbore plug structure 300 that are illustrated but not described in detail are similar to the components of the wellbore plug structures 100 and 200 described above with respect to FIG. 1 and FIG. 2, and the components may be constructed from similar materials and in similar fashion as those components described with respect to FIG. 1 and FIG. 2.

Broadly characterized, the wellbore plug structure 300 includes a tubular member 302 defining a longitudinally-extending fluid conduit 310 having a proximal fluid inlet 312 and a distal fluid outlet 314. A wiping member 304 is disposed around the tubular member 302. A piston member 306 including a piston body 316 is disposed in the fluid conduit 310. A temporary fluid stopper 308 includes a dissolvable fluid obstructing portion. A piston member 306 is disposed within a fluid conduit 310 having a proximal fluid inlet 312 and a distal fluid outlet 314.

As compared to the embodiment illustrated in FIG. 2, the temporary fluid stopper 308 includes a dissolvable body 340 that extends across the fluid conduit 310, where the dissolvable body 340 has a well 344 formed through a central portion of the body 340, e.g., along a longitudinal axis of the fluid conduit 310. In this manner, the dissolution time can be controlled by adjusting the depth of the well 344, i.e., by adjusting the thickness of the dissolvable material below the well 344.

Another feature illustrated by the wellbore plug structure 300 of FIG. 3 is that the interior wall 326 of the fluid conduit 310 includes an inward flange 328 that is disposed below the piston body 316 and above the temporary fluid stopper 308. The purpose of the inward flange 328 is to reduce the velocity of the piston body 316 when the piston release pressure forces the piston body 316 downwardly toward the temporary fluid stopper 308. Reducing the velocity of the piston body 316 will reduce the likelihood that the temporary fluid stopper 308 will become fractured by the piston body 316.

In any of the foregoing embodiments, the thickness of the dissolvable fluid obstructing portion measured along a central longitudinal axis of the fluid conduit (e.g., through the center of the obstructing portion) may be selected to control the dissolution time needed to dissolve through the dissolvable material. While not limited to any particular thickness, in certain characterizations the thickness of the dissolvable fluid obstructing portion measured along the longitudinal axis of the fluid conduit will typically be at least about 0.5 mm, such as at least about 1 mm or even at least about 5 mm. In another characterization, this thickness will typically be not greater than about 300 mm, such as not greater than about 200 mm, or not greater than about 100 mm.

FIG. 4 illustrates another embodiment of a wellbore plug structure according to the present disclosure. In the embodiments illustrated in FIGS. 1 to 3, a dissolvable material is utilized to directly block the fluid flow through the longitudinally-extending fluid conduit, e.g., by being placed directly across the fluid conduit. In the embodiment illustrated in FIG. 4, the dissolvable material is utilized in combination with a non-dissolvable component, such as a collet member, such that once the material dissolves, the collet member collapses (e.g., the collet fingers collapse inwardly), under the pressure of the fluid thereby opening up a fluid pathway through the fluid conduit from the proximal end to the distal end.

Referring to FIG. 4, the wellbore plug structure 400 includes a tubular member 402 defining a longitudinally-extending fluid conduit 410 having a proximal fluid inlet 412 and a distal fluid outlet 414. Disposed near the proximal end of the tubular member 402 is a piston member 406 that includes a piston body 416 that is at least partially disposed in the fluid conduit 410.

A collet member 470 is disposed within the fluid conduit 410. The collet member 470 includes a collet member body 472 having a distal fluid obstructing portion 480 and a plurality of fingers 478 extending therefrom, i.e., extending toward the proximal end. The proximal end of the collet member body 472 includes an internally notched portion 482 having a larger internal diameter than the portion disposed below the notched portion 482. A dissolvable ring 474 is sized and configured to be placed within the notched portion 482 and includes an aperture 484 that is sized to permit the piston body 416 to pass through the aperture 484 when subjected to a sufficiently high pressure. The dissolvable ring 474, when placed within the notched portion 482 of the collet body 472, restricts inward movement of the fingers 478 and thereby inhibits movement of the collet body in a downward direction, i.e., toward a distal end of the tubular member 402.

The collet member 470 and the piston member 406 define an interior chamber 420 within the fluid conduit 410, the interior chamber 420 being fluidly sealed from the proximal fluid inlet 412 by the piston member 406 and being fluidly sealed from the distal fluid outlet 414 by the collet member 470, i.e., by the fluid obstructing portion 480 of the collet member body 472.

As with the embodiments illustrated above in FIGS. 1 and 2, the piston member 406 is configured to release and move toward the distal fluid outlet 414 when the piston member 406 is exposed to a pressure difference across the piston member 406 that is equal to or greater than a piston release pressure. This release and movement of the piston member 406 creates a fluid pathway from the proximal fluid inlet 412 to the interior chamber 420 of the fluid conduit.

To facilitate the release and movement of the piston member 406 when exposed to the piston release pressure, the piston member 406 includes at least one shear element 424 a that operatively secures the piston body 416 within the fluid conduit 410 and is configured to shear when the piston member 406 is exposed to the requisite pressure difference across the piston member 406. It will be appreciated that the piston member 406 may include a plurality of shear elements, and as illustrated in FIG. 4, the piston member comprises at least a second shear element 424 b that is also configured to shear when the piston member is exposed to the pressure difference across the piston member that is equal to or greater than the piston release pressure. The shear elements 424 a/424 b may comprise a shear pin, shear ring, or shear wire, and in certain characterizations the shear elements 424 a/424 b are shear screws.

As illustrated in FIG. 4, the piston member 406 is fully disposed within the fluid conduit 410, although it is contemplated that the wellbore plug structure 400 could be configured such that the piston member 406 is partially disposed within the fluid conduit 410, e.g., where the piston member 406 is partially disposed outside of the fluid conduit 410.

The piston body 416 may be fabricated from virtually any material. For example, it is contemplated that the entire piston body 416, or a portion of the piston body 416, may be fabricated from a dissolvable material. In certain characterizations, the piston body 416 is at least partially fabricated from a metallic material, particularly a millable metallic material such as aluminum or cast-iron. In this regard, for certain applications, it may be preferable to utilize a piston body that is at least partially fabricated from aluminum. The piston body 416 may be substantially cylindrical, such as to operatively fit within a substantially cylindrical longitudinally-extending fluid conduit 410, or, as illustrated in FIG. 4, within a sleeve member 462 that itself is disposed within the fluid conduit 410. To ensure a substantially fluid tight seal between the piston body 416 the interior side wall of the longitudinally-extending fluid conduit 410, the piston member 406 may include a sealing component 430, e.g., a sealing component that is disposed around an outer circumference of the piston body 416. The sealing component 430 may comprise configurations such as a Chevron-type seal. In certain characterizations, the sealing component 430 includes an elastomeric O-ring. Further, the piston member 406 may include more than one sealing component 430, such as a plurality of elastomeric O-rings that are disposed around the piston body 416. Although the embodiment illustrated in FIG. 4 illustrates the use of an elastomeric O-ring as the sealing element, the piston body 416 may be configured, e.g., precision machined, to a tight tolerance such that a metal-to-metal seal may be formed between the piston body 416 and the interior surface of the longitudinally-extending fluid conduit 410 or the sleeve 462. Further, although illustrated as comprising a sealing component that is operatively affixed to the piston body 416, a sealing component may also be fixed to an interior of the longitudinally-extending fluid conduit 410 or to form a seal between the piston body 416 and the interior wall of the fluid conduit, or the sleeve member 462.

As with the embodiments illustrated in FIGS. 1 and 2, a wiping member 404 is disposed around the tubular member 402. The wiping member 404 includes at least a first wiper blade 434 a extending radially from the tubular member 402. The wiping member 404 of FIG. 4 comprises a second wiper blade 434 b and includes five wiper blades in total that extend radially from the tubular member 402. The wiping member 404 may be integrally formed with the tubular member 402, or may be a separate component that is attached to the tubular member 402. The size of the wiper blades (e.g., outer diameter of the wiper blades) is configured to form a tight fluid seal when the wellbore plug structure 400 is placed down a wellbore casing. The wiper blades may be fabricated from a flexible elastomeric material in order to form such a fluid-tight seal. During certain operations, the wiper blades may also force material that is loosely adhered to the interior wall of the wellbore casing down the wellbore casing, e.g., cement during a wellbore cementing operation.

The tubular member 420 may be fabricated from a variety of materials and in certain characterizations the tubular member is fabricated (e.g., machined) from a metallic material, such as aluminum. The wellbore plug structure 400 may also include a landing arrangement 436 disposed at a distal end of the wellbore plug structure 400, e.g., at a distal end of the tubular member 402. The landing arrangement 436 is configured to operatively engage with a latch collar (e.g., a sealing latch collar) or similar structure that is disposed near the bottom of the wellbore.

In the embodiment illustrated in FIG. 4, the collet member 470 comprises a sealing component 476 disposed around an outer circumference of the collet member body 472. The sealing component 476 may comprise, for example, an elastomeric O-ring. As illustrated in FIG. 4, the collet member 470 includes two elastomeric O-rings.

In the embodiment illustrated in FIG. 4, when the piston body 416 releases, it moves through the aperture 484 and into the collet member body 472. The movement of the piston exposes the dissolvable ring 474 to the fluid. Upon dissolution of the dissolvable ring 474, the fingers 478 are no longer restricted from moving inwardly. Therefore, when pressure is applied to the collet member body 472, the fingers 478 are forced inwardly and the entire collet member will be displaced downwardly and remove through the fluid conduit 410 and out of the distal fluid outlet 414. As a result, a fluid pathway through the entire fluid conduit 410 will be formed.

FIG. 5 illustrates yet another embodiment of a wellbore plug structure according to the present disclosure. The embodiment illustrated in FIG. 5 is similar to the embodiment illustrated in FIG. 4 in that the dissolvable material is utilized in combination with a collet member such that once the material dissolves, the collet member is exposed to the fluid pressure and collapses (e.g., the collet fingers collapse inwardly), thereby opening up a fluid pathway through the fluid conduit from the proximal end to the distal end.

Referring to FIG. 5, the wellbore plug structure 500 includes a tubular member 502 defining a longitudinally-extending fluid conduit 510 having a proximal fluid inlet 512 and a distal fluid outlet 514. Disposed within the tubular member 502 is a piston member 506 that includes a piston body 516 that is at least partially disposed in the fluid conduit 510.

A collet member 570 is disposed within the fluid conduit 510, between the piston body 516 and the distal fluid outlet 514. The collet member 570 includes a collet member body 572 having a distal fluid obstructing portion 580 and a plurality of fingers 578 extending upwardly therefrom, i.e., extending toward the proximal end. The proximal end of the collet member body 572 includes an internally notched portion 382 having a larger internal diameter than the portion disposed below the notched portion 582. A dissolvable ring 574 is sized and configured to be placed within the notched portion 582 and includes an aperture 584 that is sized to permit the piston body 516 to pass through the aperture 584 when subjected to a sufficiently high pressure. The dissolvable ring 574, when placed within the notched portion 582 of the collet body 572, restricts inward movement of the fingers 578 and thereby inhibits movement of the collet body in a downward direction, i.e., toward a distal end of the tubular member 502.

The collet member 570 and the piston member 506 define an interior chamber 520 within the fluid conduit 510, the interior chamber 520 being fluidly sealed from the proximal fluid inlet 512 by the piston member 506 and being fluidly sealed from the distal fluid outlet 514 by the collet member 570, i.e., by the fluid obstructing portion 580 of the collet member body 572.

As with the embodiment illustrated above in FIG. 4, the piston member 506 is configured to release and move toward the distal fluid outlet 514 when the piston member 506 is exposed to a pressure difference across the piston member 506 that is equal to or greater than a piston release pressure. This release and movement of the piston member 506 creates a fluid pathway from the proximal fluid inlet 512 to the interior chamber 520 of the fluid conduit.

To facilitate the release and movement of the piston member 506 when exposed to the piston release pressure, the piston member 506 includes at least one shear element, e.g., shear elements 524 a and 524 b that operatively secure the piston body 516 within the fluid conduit 510 and is configured to shear when the piston member 506 is exposed to the requisite pressure difference across the piston member 506. The shear elements 524 a/524 b may comprise a shear pin, shear ring, or shear wire, and in certain characterizations the shear elements 524 a/524 b are shear screws.

The piston body 516 may be fabricated from virtually any material as is discussed above, e.g., with respect to FIG. 4. The piston body 516 may be substantially cylindrical, such as to operatively fit within a substantially cylindrical longitudinally-extending fluid conduit 510. To ensure a substantially fluid tight seal between the piston body 516 the interior side wall of the longitudinally-extending fluid conduit 510, the piston member 506 may include a sealing component 530, e.g., a sealing component that is disposed around an outer circumference of the piston body 516. The sealing component 530 may comprise configurations such as a Chevron-type seal. In certain characterizations, the sealing component 530 includes an elastomeric O-ring, and the sealing component may include more than one element, e.g., more than one elastomeric O-ring. Although the embodiment illustrated in FIG. 5 illustrates the use of an elastomeric O-ring as the sealing element, the piston body 516 may be configured, e.g., precision machined, to a tight tolerance such that a metal-to-metal seal may be formed between the piston body 516 and the interior surface of the longitudinally-extending fluid conduit 510. The sealing component may also be fixed to an interior of the longitudinally-extending fluid conduit 510 such as to form a seal between the piston body 316 and the interior wall of the fluid conduit.

The tubular member 520 may be fabricated from a variety of materials as is discussed above with respect to FIG. 3. The wellbore plug structure 500 may also include a landing arrangement 536 disposed at a distal end of the wellbore plug structure 500, e.g., at a distal end of the tubular member 502. The landing arrangement 536 is configured to operatively engage with a latch collar (e.g., a sealing latch collar) or similar structure that is disposed near the bottom of the wellbore.

In the embodiment illustrated in FIG. 5, when the piston body 516 releases, it moves through the aperture 584 and into the collet member body 572, e.g., into the interior chamber 520. The movement of the piston body 516 exposes the dissolvable ring 574 to the fluid. Upon dissolution of the dissolvable ring 574 by the fluid, the fingers 578 are no longer restricted from moving inwardly. Therefore, when pressure is applied to the collet member body 572 (e.g., directly against the fluid obstructing portion 580), the fingers 578 are forced inwardly and the entire collet member will be displaced downwardly, moving through the fluid conduit 510 and out of the distal fluid outlet 514. As a result, a fluid pathway through the entire fluid conduit 510 will advantageously be formed.

The wellbore plug structures illustrated in FIGS. 1 to 5 are particularly useful for the pressure testing of a completed wellbore, e.g., integrity testing of the casing. In one embodiment, a method of pressure testing a wellbore is provided, where the method includes inserting the wellbore plug structure into a wellbore casing where the wellbore plug structure includes a tubular member defining a longitudinally-extending fluid conduit having a proximal fluid inlet and a distal fluid outlet, a wiping member disposed around the tubular member, a piston member comprising a piston body that is at least partially disposed in the fluid conduit, and a dissolvable element disposed in the fluid conduit. For example, the dissolvable element may include a portion that is disposed completely across the fluid conduit to block fluid flow (FIGS. 1 to 3), or may be an element that holds another component in the fluid conduit (e.g., FIGS. 4 and 5) The wellbore is pressurized to a first wellbore pressure to advance the wellbore plug structure down the wellbore, i.e., down the casing. Thereafter, at any time after placement of the structure in the wellbore, the wellbore is pressurized with a pressurizing fluid to a second wellbore pressure that is greater than the first wellbore pressure. The second wellbore pressure (e.g., the piston release pressure) displaces the piston member downwardly into the fluid conduit and exposes the dissolvable element to the pressurizing fluid. Pressure testing of the wellbore (casing integrity test) may then be completed at a third wellbore pressure before the pressurizing fluid completely dissolves the dissolvable element. Once the fluid dissolves the dissolvable element, a fluid passageway is opened through the wellbore plug structure, and tooling may be passed through the wellbore plug structure.

In one characterization, the step of pressurizing the wellbore casing to a first wellbore pressure to advance the wellbore plug structure down the well bore includes landing a distal end of the wellbore plug structure onto a stop collar that disposed in the wellbore, e.g., is disposed around a circumference of the casing. In another characterization, the wellbore plug structure is utilized during a cementing operation. Thus, during the step of pressurizing the wellbore casing to a first wellbore pressure to advance the wellbore plug structure down the wellbore, the wellbore plug structure forces a cementing composition down the wellbore.

While various embodiments of a wellbore plug structure and a method for pressure testing a wellbore have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present disclosure. 

1. A wellbore plug structure, comprising: a tubular member defining a longitudinally-extending fluid conduit having a proximal fluid inlet and a distal fluid outlet; a wiping member disposed around the tubular member; a piston member comprising a piston body that is at least partially disposed in the fluid conduit; and a temporary fluid stopper comprising a dissolvable fluid obstructing portion, where the dissolvable fluid obstructing portion is disposed in spaced-apart relation from the piston member toward the distal fluid outlet; wherein the piston member and the dissolvable fluid obstructing portion define an interior chamber within the fluid conduit, the interior chamber being fluidly sealed from the proximal fluid inlet by the piston member and being fluidly sealed from the distal fluid outlet by the dissolvable fluid obstructing portion.
 2. The wellbore plug structure recited in claim 1, wherein the piston member is configured to release and move toward the distal fluid outlet when the piston member is exposed to a pressure difference across the piston member that is equal to or greater than a piston release pressure.
 3. The wellbore plug structure recited in claim 2, wherein the release and movement of the piston member creates a fluid pathway from the proximal fluid inlet to the interior chamber of the fluid conduit.
 4. The wellbore plug structure recited in claim 1, wherein the piston member comprises at least one shear element, wherein the at least one shear element operatively secures the piston member within the fluid conduit and is configured to shear when the piston member is exposed to the pressure difference across the piston member that is equal to or greater than the piston release pressure to release the piston body.
 5. (canceled)
 6. (canceled)
 7. The wellbore plug structure recited in claim 1, wherein the piston member is fully disposed within the fluid conduit. 8-12. (canceled)
 13. The wellbore plug structure recited in claim 1, wherein the wiping member comprises at least a first wiper blade extending radially from the tubular member. 14-16. (canceled)
 17. The wellbore plug structure recited in claim 1, wherein the dissolvable fluid obstructing portion is disposed across the fluid conduit.
 18. The wellbore plug structure recited in claim 1, wherein the dissolvable fluid obstructing portion is fabricated from a material that is dissolvable in an aqueous medium.
 19. The wellbore plug structure recited in claim 1, wherein the dissolvable fluid obstructing portion is fabricated from a material that is dissolvable in an aqueous chloride solution. 20-22. (canceled)
 23. The wellbore plug structure recited in claim 1, wherein the dissolvable fluid obstructing portion has a thickness measured along a longitudinal axis of the fluid conduit that is at least about 0.5 mm. 24-30. (canceled)
 31. The wellbore plug structure recited in claim 1, wherein the temporary fluid stopper comprises a cup-like temporary fluid stopper body comprising the dissolvable fluid obstructing portion and a wall portion extending from a circumferential edge of the dissolvable fluid obstructing portion along an interior wall of the fluid conduit. 32-34. (canceled)
 35. The wellbore plug structure recited in any of claim 31, wherein the temporary fluid stopper body and the dissolvable fluid obstructing portion comprise the dissolvable material.
 36. The wellbore plug structure recited claim 1, wherein the dissolvable fluid obstructing portion comprises a dissolvable disk body.
 37. The wellbore plug structure recited in claim 36, wherein the dissolvable disk body is disposed across the longitudinally-extending fluid conduit. 38-41. (canceled)
 42. The wellbore plug structure recited in claim 36, wherein the fluid conduit comprises at least a first conduit portion and a second conduit portion, the second conduit portion having a larger diameter than the first conduit portion, wherein the first conduit portion is disposed near the proximal end of the fluid conduit and wherein the piston member is at least partially disposed within the first conduit portion.
 43. A wellbore plug structure, comprising: a tubular member defining a longitudinally-extending fluid conduit having a proximal fluid inlet and a distal fluid outlet; a wiping member disposed around the tubular member; a piston member comprising a piston body that is at least partially disposed in the fluid conduit; a collet member at least partially disposed within the fluid conduit, the collet member comprising a collet member body, the collet member body comprising a plurality of collet fingers, and a dissolvable ring component disposed within the collet body to resist inward collapse of the collet fingers; wherein the collet member and the piston member define an interior chamber within the fluid conduit, the interior chamber being fluidly sealed from the proximal fluid inlet by the piston member and being fluidly sealed from the distal fluid outlet by the collet member.
 44. The wellbore plug structure recited in claim 43, wherein the piston member is configured to release and move toward the distal fluid outlet when the piston member is exposed to a pressure difference across the piston member that is equal to or greater than a piston release pressure.
 45. The wellbore plug structure recited in claim 44, wherein the release and movement of the piston member creates a fluid pathway from the proximal fluid inlet to the interior chamber of the fluid conduit.
 46. The wellbore plug structure recited in claim 43, wherein the piston member comprises at least one shear element, wherein the at least one shear element operatively secures the piston member within the fluid conduit and is configured to shear when the piston member is exposed to the pressure difference across the piston member that is equal to or greater than the piston release pressure to release the piston body.
 47. (canceled)
 48. (canceled)
 49. The wellbore plug structure recited in claim 43, wherein the piston member is fully disposed within the fluid conduit. 50-54. (canceled)
 55. The wellbore plug structure recited in claim 43, wherein the wiping member comprises at least a first wiper blade extending radially from the tubular member. 56-68. (canceled) 